Class III antiarrhythmic agents may be categorized as having the ability to markedly prolong cardiac action potential duration without producing significant changes in maximal upstroke velocity. Unlike Class I antiarrhythmic agents, a pure Class III agent displays no effect on cardiac sodium channels. The electrophysiologic properties of a compound defining a Class III activity profile are observed in vivo as negligible effects on atrial, ventricular and H-V conduction times while producing a marked increase (greater than 20 percent) in both the atrial and ventricular refractory period. In contrast, Class I agents will demonstrate a marked slowing of ventricular conduction velocity, often without significant changes in the refractory period. Recent reviews of these agents are: Bexton et al.; Pharmac. Ther. 17, 315-55 (1982); Vaughan-Williams, J. Clin. Pharmacol. 24, 129-47 (1984); Steinberg et al., Ann. Rep. Med. Chem. 21, 95-108 (1986) and Colatsky and Follmer, Drug Development Research 19; 129-140 (1990).
Buzby et al. recently disclosed 4-methylsulfonamido-N-[2-[(1-methylethyl)amino]ethyl]benzenesulfonamide as a potential Class III antiarrhythmic agent in U.S. Pat. No. 4,721,809, Jan. 26, 1988.
Davey et al. disclosed N-[2-(diethylamino)ethyl-4-[(methylsulfonyl)amino]benzamide as a potential Class III antiarrhythmic agent in U.S. Pat. No. 4,544,654, Oct. 1, 1985.
Winkley et al. disclosed N-[4-[(2,3,5,6-tetrahydro-[1,3,6]triazocino[1,2-a]benzimidazol-4-(1H)-yl)s ulfonyl]phenyl]methanesulfonamide as a potential Class III antiarrhythmic agent in U.S. Pat. No. 4,882,323, Nov. 21, 1989.
The compounds of the present invention differ from those disclosed by Buzby et al. and Davey et al. by the presence of a nitrogen containing heterocycle (R.sup.4 in general formula (I) below). They differ from the compounds disclosed by Winkley et al. in that they lack a triazocino group.